1. Field of the Invention
The present invention relates to a film forming method for continuously forming a desired film on a surface of a substrate selected from various kinds of materials such as macromolecular materials, metals, glass, ceramics, etc., and an apparatus therefor.
2. Description of the Related Art
In recent years, film forming using vacuum evaporation of a particular material onto the surface of a substrate has been widely adapted for forming a metal film as a printed wiring precursor onto a printed wiring substrate formed from a macromolecular material, forming a of a corrosion-resisting film onto a surface of a substrate formed from stainless steel or the like, and forming of a semiconductor film onto a liquid crystal display glass substrate, for example. Such vacuum evaporation film forming has an advantage in that the film forming speed is relatively high compared with film forming using sputtering or the like.
Vacuum evaporation film forming, however, has a problem in that mutual adhesion at the interface between the substrate surface and the film formed thereon is to weak that the film may be separated from the substrate when the substrate is processed after the film is formed. For example, where an aluminum film for printed wiring is formed on a surface of a printed wiring substrate formed of a polyimide film, a problem arises in that the aluminum film may be separated by exposure of the film to high or low temperature after the film is formed. In the case where a corrosion-resisting aluminum film is formed on a stainless steel substrate, for example, the aluminum film may be broken or separated when the stainless steel substrate is processed by bending, pressing or the like after the film is formed.
A method has been heretofore proposed to solve the aforementioned problems and in which vacuum evaporation of a particular material onto a surface of a substrate and ion radiation are used in combination to form an adhesive mixed layer of constituent atoms of the substrate material and constituent atoms of an evaporated material on a portion of the substrate surface to form an evaporation film of the same material and of a predetermined thickness on the mixed layer with good adhesion.
In forming the mixing layer to improve the adhesion, all the thickness of the resulting film is not necessary. That is, a film with an arbitrary thickness is formed by vacuum evaporation after the mixing layer is formed by ion radiation adjacent to the interface between the substrate and the film.
In such a film forming process using a combination of vacuum evaporation and ion radiation, continuous movement of a strip-like or plate-like substrate has been proposed for the purpose of film forming efficiency.
FIG. 5 shows an example of an apparatus for performing such continuous film forming, in which a vacuum vessel 9 capable of being kept in a predetermined vacuum by an exhaust device (not shown), is partitioned into two portions 91 and 92. One portion 91 is used for a material evaporation source 93 and an ion source 94 for forming a mixed layer, and the other portion 92 is used for a material evaporation source 95 for forming an evaporation film of predetermined thickness on the mixed layer. A substrate 96 is passed from the one portion 91 to the other portion 92 so that the mixed layer is formed at the portion 91 and then the evaporation film of predetermined thickness is formed at the portion 92.
The reason why the vacuum vessel 9 is partitioned into two film forming portions 91 an 92 is that if the film forming condition is suited to the moving speed of the substrate, it is necessary to reduce the speed of evaporation to satisfy the quantity of ion radiation in the mixed layer forming step. If the total film forming speed is increased, it is necessary to change the speed of evaporation between the mixed layer forming step and the evaporation film forming step.
Another method and apparatus have been proposed as described in Japanese Patent Unexamined Publication No. Sho-60-141869. In this proposed film forming method and apparatus, a first ion source, a first evaporation source, a second ion source and a second evaporation source (which may be combined with an ion plating means) are disposed in a vacuum vessel along the direction of substrate feed to carry out a pretreatment, such as cleaning, of the substrate surface using the first ion source, form an evaporation film for forming a mixed layer using the first evaporation source, form the mixed layer by ion radiation with the second ion source and form an evaporation film of a predetermined thickness on the mixed layer with the second evaporation source.
In the film forming method and apparatus described in each of FIG. 5 and Japanese Patent Unexamined Publication No. Sho-60-1414869, not only at least one ion source and one evaporation source are necessary for forming the mixed layer, but at least one evaporation source is also necessary for forming the evaporation film. Thus, a problem is present in that the number of evaporation sources is increased and film forming cost is increased.
In the method and apparatus described in Japanese Patent Unexamined Publication No. Sho-60-141869, the mixed layer is formed by performing ion injection with the second ion source after forming the evaporation film using the first evaporation source. Accordingly, ion energy due to the second ion source must be enlarged. Otherwise, great reduction of the substrate feeding speed may be considered, but production efficiency is compromised if the substrate feeding speed is reduced greatly.